Crosstalk at Angular Incidence

imagesensorex03.in : Crosstalk at Angular Incidence

Requires: Blaze/Luminous
Minimum Versions: Atlas 5.28.1.R

In this example we attempt to look at the crosstalk between adjacent colors due to angularly incident light. In this case we simulate two adjacent pixels; one red and one green. We then obtain solutions as a function of angle of incidence and collect the integrated photogeneration rate as a measure of the relative charge collected in each of the adjacent pixels. This measure can be used to quantify crosstalk as a function of angle of incidence.

The simulations begins with a description of the device structure and mesh using the MESH , X.M , Y.M , REGION , ELEC , and DOPING statements.

In this example we add a couple of extra oxide regions to represent the color filters for the adjacent pixels. The optical characteristics of these regions will be modified to pass or not pass the source light.

Next, we specify some material models and parameter defaults. Of significance is the specification of the complex index of refraction of aluminum using the REAL.INDEX and IMAG.INDEX parameters of the MATERIAL statement. In this case we set the imaginary index to a very high value. This makes the aluminum blocking regions highly reflective/absorptive to light.

Here we also specify the imaginary index of the red filter. In this case the thickness of the filter was used to calculate an index that will absorb 99% of the incident light. We do not need to specify the index of the green filter since it is assumed to pass all of the incident light.

Next we specify the optical source on the BEAM statement. We specify the light with normal incidence from above with a wavelength of 0.5325 microns. This wavelength corresponds to the band pass of the green filter. We also define the sampling in the FDTD mesh. This sampling should typically be a small fraction of the incident wavelength. The TD.WAVES parameter specifies how many source wavelengths are propogated in this simulation. Finally, we specify a file for capture of the structure as represented in the final FDTD mesh solution. This is useful to examine the interference and diffraction patterns that might not be otherwise discernable in the standard finite-difference structure file.

Next, we specify the lenslets above the two pixels.

We add perfectly matched layers (PMLs) at the top and bottom of the FDTD domain to absorb reflected and transmitted light. This is specified on the PML statements.

After obtaining the initial solution, we define probes using the PROBE statement to allow us to measure the integrated photogeneration rate as a function of wavelength in both of the green and red sensor wells. It is important to notice that we specified the FDTD parameter on the PROBE statement. This indicates that the integration of the generation rate will take place in the FDTD analysis domain. The FDTD domain presents a more accurate estimate since some loss is expected during interpolation to the finite-difference domain.

Finally, we capture the solutions for various angles as specified by the ANGLE parameter of the SOLVE statement. These angles were selected to provide integer numbers of wavelengths in phase shift at the edges of the source.

When the simulation is complete we can look at the integrated photogeneration rates in the adjacent wells as a function of angle of incidence. Here we can see that after about 20 degrees, the collected green rate decreases and the collected red rate begins to increase. This information is very useful in designing the collection system of the camera.

To load and run this example, select the Load button in DeckBuild > Examples. This will copy the input file and any support files to your current working directory. Select the Run button in DeckBuild to execute the example.